Commercial and industrial buildings frequently incorporate air-handling equipment for heating, ventilating and air conditioning purposes. In a typical HVAC application, movement of large quantities of air is facilitated by strong but lightweight enclosures which may house fans, motors, cooling elements, heating elements and/or humidifying elements. Because such enclosures are frequently roof-mounted, and because such enclosures gain utility by being portable, it is desirable that they be lightweight. At the same time, because the air-handling process typically involves creation of areas of high pressure or low pressure, it is desirable that HVAC enclosures feature relatively high strength in the walls, floors and tops.
Another important feature of this type of enclosure, in addition to the ability to withstand deformation under internal air pressures, is that such enclosures exhibit certain thermal insulating properties.
Enclosures of the type described are typically made of lightweight metals, such as aluminum, which has poor thermal insulating qualities. While aluminum has a high strength to weight ratio, in order to produce enclosures within optimum strength-to-weight ratios, relatively thin aluminum must be used. To enhance the strength of the enclosure using aluminum of this dimension, it is known to form the aluminum enclosure from aluminum sheets which are bent or otherwise formed to create essentially box-like panels of predetermined length, width and depth. Typically, the panel so formed is then filled with an insulating foam such as polyurethane. The resulting structure is a strong, lightweight building element, which can be cooperatively assembled with a collection of similar elements to form the walls, floor or ceiling of the enclosure.
In the prior art, the exterior surface of the completed enclosure is typically made of sheet aluminum, and is secured to the elements above-described. It is desirable, however, that this exterior surface be thermally insulated from the remaining elements of the closure. To accomplish this, prior art enclosures utilize a pair of aluminum extrusions which are joined together by a thermoplastic element having acceptable insulating qualities. In this fashion, the exposed exterior of the completed enclosure is thermally insulated from the interior of the enclosure. While this technique is useful, the design of the prior art structure includes placement of fasteners, bottom supports and top supports which allow transmission of heat energy from the interior to the exterior of the structure, hence reducing the insulating efficiency of the structure.
There is a need, therefore, for an improved wall structure for HVAC enclosures which minimizes the transmission of thermal energy from the interior to the exterior of the enclosure, while still maintaining the high strength and low weight of the completed enclosure.